The proposed research will continue investigations of methods for cyclizing gamma-alkylthiopropylamines and related substances to form S-alkylisothiazolidines. Similar studies will explore the possibilities of intramolecular attack on sulfur by carboxyl and hydroxyl groups during oxidation of sulfur. Previous work has confirmed that methionine cyclizes to form dehydromethionine in which an azasulfonium (N-protonated sulfilimine) linkage exists between nitrogen and sulfur. The sulfur in these substances is chiral. We have shown that dehydromethionine is readily reduced by thiols in a nucleophilic attach of the latter on the sulfonium group of dehydromethione. Future work will attempt to oxidize dehydromethionine to a sulfoximine and to induce molecular rearrangements under conditions conducive to formation of a N-S ylide. The mechanisms of acid-base catalysis of the thiol-dehydromethionine will be studied. The biological activity of S-alkylisothiazolidines will be investigated. Dehydromethionine may be a mild oxidant of sulfhydryls in enzymes. S-alkylisothiazolidines and acyloxosulfonium salts will be tested for possible ability to induce formation of phosphate anhydrides in model reactions for oxidative phosphorylation. The principal objective of the proposed research is to discover and elucidate mechanisms by which the sulfur of methionine may participate in biologically important reactions. A secondary objective is to develop synthetic methods which may lead to pharmacologically active compounds.